Knowing which supplements to take can be confusing, especially when you’re confronted with multiple forms of the same vitamin lined up along the aisles. If you know you’re supposed to take vitamin D but aren’t sure whether you should take vitamin D2 vs D3 supplements, we tapped experts to explain the key differences.
The good news: they aren’t that different. One form tends to be easier for your body to absorb, but there are some cases in which a doctor might suggest taking the other form of the vitamin. But both vitamin D2 and vitamin D3 can help your body absorb calcium.
In addition to taking supplements recommended by your healthcare provider, you can also increase your vitamin D intake by eating certain foods. Mushrooms are a good source of vitamin D2 and certain foods, such as plant-based milks and breakfast cereals, are often fortified with vitamin D2. Fatty fish and egg yolks are a good source of vitamin D3, and you’ll also often find food products that are fortified with this form of the vitamin.
Ahead, learn more about vitamin D2 vs D3 supplements to find out which one you should be taking. Plus, experts explain what to know about safe dosages and why doctors may prescribe one over the other.
Vitamin D2 vs vitamin D3
Let’s start here: What is the difference between D2 and D3? ‘People get confused about D2 and D3 because they have heard about multiple B vitamins, like B9 and B12,’ says Carol Haggans, a scientific and health communications consultant in the NIH Office of Dietary Supplements. ‘Those different B vitamins are actually distinctly different nutrients.’ Vitamin B9, for example, is folate, which is recommended for pregnant women to prevent birth defects; B12 is cobalamin, which works to keep your blood and nerve cells healthy, and helps make DNA.
Vitamin D2 and D3, however, are not different nutrients. ‘They are essentially the same compound,’ says Carol, with only a slight chemical difference in their side chain structure. Still, while both are vitamin D and can help you raise your blood levels, they’re not exactly the same.
Vitamin D3
Is called cholecalciferolD3 is what your body produces when your skin is exposed to sunlightIt can also be found in fish (fatty ones such as trout, salmon, tuna and mackerel) and fish liver oils, as well as other animal products.It is the version most often used in fortified foods, such as milk, cereal and orange juice, says Carol.D3 supplements are made from an irradiated compound in lanolin, which comes from sheep wool (though there is an animal-free version made from lichen)
Vitamin D2
Is called ergocalciferolYou can only get it by eating fortified food or dietary supplements (not from sunlight)D2 supplements are derived from plant products, specifically a compound in yeast that has been zapped with UV lightIt can sometimes be found in mushrooms, particularly those that are treated with UV-light to up their D2 content Plant-based foods are often fortified with D2, though many cereals and orange juices have D3 Is it better to take vitamin D3 supplements instead of D2?
To be clear: both forms of vitamin D help you absorb calcium, which is key for the health of your bones. Your muscles and nerves need it to function, and it helps to support your immune system. But ‘Vitamin D3 is more bioavailable (aka has a stronger ability to be absorbed and used in the body), which is why people tend to prefer vitamin D3,’ says Dr JoAnn Manson, a professor of medicine at Harvard Medical School and chief of the Division of Preventive Medicine at Brigham and Women’s Hospital in Boston.
When researchers had folks take the vitamin D2 and D3 at the levels most people take, ‘There was a greater rise in the blood levels of vitamin D3,’ she says, which is how they know if you have sufficient amounts to keep you well. ‘There is evidence that D3 increases serum levels better, and that vitamin D levels maintain those higher levels longer than D2,’ agrees Carol.
That said, both vitamin D3 and D2 are well absorbed in the gut, and both work well to raise blood levels of vitamin D. ‘It’s not a tremendous difference – it’s not like [D3 is] twice as bioavailable as D2,’ says Dr Manson, who adds that it’s hard to precisely measure the effects of each supplement in the blood because people get vitamin D in other ways, such as through sun exposure and food.
One thing to keep in mind: Vitamin D2 supplements are derived from plant materials, so if you follow a vegan diet or avoid animal products for other reasons, D2 is a better choice for you. D2 is sometimes added to plant-based products. ‘Most fortified products will indicate what form of vitamin D they used,’ says Carol. If you don’t see it indicated on the label of food or supplements, contact the manufacturer, who should be able to tell you.
Why do doctors prescribe vitamin D2 instead of D3?
They don’t always, and for most people, D3 is a better option because it is more effective in raising your blood levels when you supplement daily, says Dr Manson.
But if someone needs a bolus dose (that is, a very high dose given over a short period of time to correct a deficiency) doctors sometimes use D2, says Dr Manson, as it has historically been available in very high doses.
Keep in mind: You should never take large doses of either form of vitamin D unless your doctor specifically prescribes it. ‘You don’t want to go on anything above the upper limit for any length of time,’ says Carol. (For healthy people between 12 months and 70 years of age the recommended daily dose is 600 IU, but Dr Manson’s research indicates that it is safe to take 1,000-2,000 IU a day ‘as a type of insurance’ to make sure you’re getting enough, she says.) Under no circumstances, says Dr Manson, should you exceed 4,000 IU of vitamin D in a day, including all sources. Very high levels can cause vomiting, muscle issues, pain and confusion, among other things, according to the NIH.
If your doctor recommends a supplement, it’s wise to ask how much to take and when your blood will be next checked to make sure your levels have been raised sufficiently, says Carol. ‘You might only need to for a period of time to boost levels up,’ she adds.
Bottom line: it doesn’t much matter which you take, unless you want to avoid animal products, says Dr Manson, in which case D2 is a better choice. D3 is better at raising blood levels of vitamin D, but D2 also works well. The main thing, says Dr Manson, is to take whichever you choose along with a bit of food that contains fat. That’s because vitamin D is absorbed better with fat, and explains why one formulation you’ll see in the vitamin aisle is gel caps containing oil. As with all supplements, choose your brands carefully.
Stefani (she/her) is a registered dietitian, a NASM-certified personal trainer and the director of the Good Housekeeping Institute Nutrition and Fitness Lab, where she oversees all nutrition and fitness-related content, testing and evaluation. She holds a master’s degree in clinical nutrition from New York University, as well as advanced certifications as a Women’s Fitness Specialist and a Behavior Change Specialist. Stefani is dedicated to providing readers with evidence-based content to encourage informed food choices and healthy living. She is an avid CrossFitter and a passionate home cook who loves spending time with her big fit Greek family.